1. Field of the Invention
The present invention relates to an ink set, a process for forming a colored portion and an ink-jet recording apparatus, and particularly to an ink set which can form excellent ink-jet recorded articles that have a wide color reproduction range, are excellent in color uniformity, do not cause bleeding between inks of different colors, have little stripe irregularity at solid printed areas and also have good weather resistance (light fastness, gas (ozone) fastness and water fastness) and rub-off resistance on plain paper, a process for forming a colored portion and an ink-jet recording apparatus.
2. Related Background Art
The conventional inks used in ink-jet recording methods generally comprise water as a principal component and a water-soluble high-boiling solvent such as a glycol for the purpose of preventing drying of the inks and clogging of orifices. When such an ink is used to conduct recording on a recording medium, therefore, such problems that sufficient fixing ability is not achieved, and an uneven image occurs, which is considered to be attributable to uneven distribution of a filler and/or a size on recording paper as a recording medium, may arise in some cases.
On the other hand, in recent years, there has been a strong demand for requiring high image quality of the same level as that of a silver salt photograph for ink-jet recorded articles. There have hence been very high technical demands for heightening the optical density of ink-jet recorded images, widening a color reproduction range and improving the color evenness of the recorded articles.
Under such circumstances, various proposals have heretofore been made for the purpose of stabilizing an ink-jet recording process and improving the quality of recorded articles by the ink-jet recording process. As one of proposals as to recording media, has proposed a method of coating the surface of a paper substrate of a recording medium with a filler and/or a size. For example, disclosed herein are techniques in which porous fine particles, which adsorb a coloring material, are coated as the filler on the paper substrate to form an ink-receiving layer by the porous fine particles. Coated paper for ink-jet, and the like are sold as recording media using these technique. Some of other representative proposals are described below.
(1) Methods of Adding a Volatile Solvent or Penetrable Solvent into an Ink:
As a means for improving the fixing ability of an ink to a recording medium, Japanese Patent Application Laid-Open No. 55-65269 discloses a method of adding a compound capable of enhancing penetrability, such as a surfactant, to an ink. Japanese Patent Application Laid-Open No. 55-66976 discloses the use of an ink comprising a volatile solvent as a main component.
(2) Methods of Mixing an Ink and a Liquid Composition, which Reacts with the Ink, on a Recording Medium:
In order to improve an optical density and water fastness of an image, and prevent bleeding, there have been proposed methods of applying a liquid composition, which can improve the image, to a recording medium prior to jetting of an ink or after the jetting.
For example, Japanese Patent Application Laid-Open No. 63-60783 discloses a method in which a liquid composition containing a basic polymer is applied to a recording medium, and recording is then conducted with an ink containing an anionic dye. Japanese Patent Application Laid-Open No. 63-22681 discloses a recording method in which a first liquid composition containing a reactive chemical species and a second liquid composition containing a compound capable of reacting with the reactive chemical species are mixed on a recording medium. Further, Japanese Patent Application Laid-Open No. 63-299971 discloses a method in which a liquid composition containing an organic compound having two or more cationic groups per molecule is applied to a recording medium, and recording is then conducted with an ink containing an anionic dye. Japanese Patent Application Laid-Open No. 64-9279 discloses a method in which an acidic liquid composition containing succinic acid or the like is applied to a recording medium, and recording is then conducted with an ink containing an anionic dye.
Further, Japanese Patent Application Laid-Open No. 64-63185 discloses a method in which a liquid composition, which insolubilizes dyes, is applied to a recording medium prior to application of an ink. Further, Japanese Patent Application Laid-Open No. 8-224955 discloses a method in which a liquid composition containing cationic substances different in molecular weight distribution range from each other is used together with an ink containing anionic compound. Japanese Patent Application Laid-Open No. 8-72393 discloses a method in which a liquid composition containing a cationic substance and finely ground cellulose is used together with an ink. In both publications, it is described that an image high in optical density and good in image quality and water fastness and also in color reproducibility and resistance to bleeding is obtained. Further, Japanese Patent Application Laid-Open No. 55-150396 discloses a method in which recording is conducted with a dye ink on a recording medium, and a water-proofing agent, which forms lake with a dye, is then applied, to propose that water fastness is imparted to the resulting recorded image.
(3) Methods of Mixing an Ink with a Liquid Composition Containing Fine Particles on a Recording Medium:
Japanese Patent Application Laid-Open No. 4-259590 discloses a method in which a colorless liquid containing colorless fine particles composed of an inorganic substance is applied to a recording medium, and an non-aqueous recording liquid is then applied. Japanese Patent Application Laid-Open No. 6-92010 discloses a method in which a solution containing fine particles or a solution containing fine particles and a polymeric binder is applied to a recording medium, and an ink containing a pigment, a water-soluble resin, a water-soluble solvent and water is then applied. In both publications, it is described that an image good in image quality and coloring properties is obtained irrespective of the kind of recording paper.
(Background Art)
The present inventors have repeatedly carried out investigations as to such various ink-jet recording techniques as described above. As a result, it has been found that although excellent effects can be recognized with respect to their respective technical objects, other ink-jet recording properties may be deteriorated in some cases in exchange for it. For example, the above-described recording medium (hereinafter referred to as coated paper) obtained by coating the surface of a paper substrate of a recording medium with a filler and/or a sizing agent is recognized as a technique with which a high-quality image can be formed.
In general, in order to obtain an image high in saturation, it has been known that a coloring material is preferably retained on the surface of a recording medium in a monomolecular state without being aggregated. Porous fine particles on the coated paper have such that function. In order to achieve high optical density and saturation of the image by a coloring material in an ink applied, however, it is indispensable to form such a thick ink-receiving layer that the paper substrate is covered with a great amount of the porous fine particles. As a result, there has been offered a problem that the texture of the paper substrate is lost. The present inventors have inferred that the necessity of such a thick ink-receiving layer that the texture of the paper substrate is lost is attributable to the fact that the coloring material is not effectively adsorbed on the porous fine particles.
Assuming coated paper having an ink-receiving layer, it will be explained in the following description. FIG. 9 typically illustrates a section of the coated paper in the vicinity of the surface thereof. In FIG. 9, reference numerals 901 and 903 indicate a paper substrate and an ink-receiving layer, respectively. The ink-receiving layer 903 generally has porous fine particles 905 and an adhesive 907 for immobilize them. When an ink is applied to the ink-receiving layer 903, the ink penetrates into voids among the porous fine particles 905 by a capillary phenomenon to form ink-penetrated portions 909. As illustrated in FIG. 9, the porous fine particles in the ink-receiving layer are topically different in density from each other, and so the penetration of the ink by the capillary phenomenon varies with the locality. Therefore, the coloring material cannot evenly contact with the surfaces of the porous fine particles in the course of the penetration of the ink, so that the coloring material is not efficiently adsorbed on the porous fine particles.
Further, the penetration of the ink is partially prevented by the adhesive 907, and so portions into which the ink cannot penetrate are present in the ink-receiving layer 903, and portions which cannot contribute to coloring are thus produced. More specifically, in the conventional coated paper, the coloring material cannot be efficiently adsorbed in a monomolecular state according to the amount of the porous fine particles for the above-described reasons. As a result, a great amount of the porous fine particles are required to provide a high-quality image, so that the texture of the paper substrate is impaired.
Although the fixing ability of an ink to a recording medium is improved by adopting the above technique (1), the optical density of an image formed and a color reproduction range, which is important for recording on plain paper and recording of color images, may have been lowered in some cases. According to the technique (2), a coloring material in an ink can be kept on the surface of a recording medium, and so a recorded article having high in optical density of images can be provided. However, a color reproduction range and saturation may have been lowered in some cases, which would be considered to be attributable to aggregation of a coloring material on the surface of a recording medium. According to the prior art described in the item (3), the surface profile of a recording medium is improved by application of the solution containing fine particles. However, any high-definition image of the same level as in coated paper has been unable to be obtained. In the non-aqueous recording liquid in particular, problems are left on its degree of freedom because selectivity of a coloring material, application method of a recording liquid, etc. are limited. Since some problems have been left on the conventional methods as described above, the present inventors have come to have recognition that the development of new ink-jet recording techniques is necessary for ink-jet recorded articles of higher quality required in recent years.
In the development of coloring materials of inks for office or personal ink-jet printers on the other hand, the development of a pigment system has also been vigorously made together with a dye system, which has been the main system over a long period of time, in recent years. In particular, there is a strong demand for future development from the viewpoint of high weather resistance (water fastness, light fastness and gas (ozone) fastness) which is characteristic of the pigment system.
Inks using black carbon black have been already put to practical use at present. However, inks using organic pigments of chromatic colors such as cyan, magenta and yellow have not yet been realized in the field of office and personal printers in respects of coloring of recorded images, and the like though they have been realized in large-size printers and the like utilized for posters and advertisements. However, the development of a production process of fine particles has been advanced in chromatic organic pigments used in ink-jet in recent years, and so-called ultrafinely particulate color organic pigments have appeared. The ultrafinely particulate color organic pigments are improved in print quality such as coloring ability and transparency on recording media such as coated paper and glossy paper for ink-jet, which have heretofore been poor compared with dye inks. However, such pigments have not succeeded in forming recorded images having sufficient coloring property on recording media poor in liquid absorbency and pigmenting, such as plain paper.
The present inventors have carried out investigations repeatedly on the basis of such findings as described above. As a result, it has been found that an aqueous liquid composition containing fine particles having an action of adsorbing a coloring material on its surface, and an aqueous ink containing an ultrafinely particulate pigment are used, and the liquid composition is brought into contact with the ink in a liquid state, whereby the ultrafinely particulate pigment efficiently reacts with the fine particles to improve the optical density and saturation of an image formed on a recording medium poor in liquid absorbency and pigmenting, such as plain paper and to bring about an excellent inhibitory effect on bleeding, thus leading to completion of the present invention.
It is therefore an object of the present invention to provide an ink set used in providing a high-quality ink-jet recorded article, a process for forming a colored portion and an ink-jet recording apparatus.
Another object of the present invention is to provide an ink set which can form excellent ink-jet recorded articles that have a wide color reproduction range, are excellent in color uniformity, do not cause bleeding between inks of different colors, have little stripe irregularity at solid printed areas and also have good weather resistance (light fastness, gas (ozone) fastness and water fastness) and rub-off resistance on plain paper, a process for forming a colored portion and an ink-jet recording apparatus.
The above objects can be achieved by the present invention described below.
In an embodiment of the present invention, there is provided an ink set comprising an aqueous ink containing at least an ultrafinely particulate pigment as a coloring material and an aqueous liquid composition containing fine particles dispersed therein and electrically charged at the surface in a polarity opposite to the ink, in a dispersed state.
In another embodiment of the present invention, there is provided a process for forming a colored portion, comprising the steps of:
(i) applying an anionic or cationic aqueous ink containing an ultrafinely particulate pigment as a coloring material to a recording medium; and
(ii) applying an aqueous liquid composition containing fine particles dispersed therein and electrically charged at the surface in a polarity opposite to the aqueous ink, in a dispersed state to the recording medium,
wherein the ink and the liquid composition are applied so as to come into contact with each other in a liquid state on the surface of the recording medium.
In a further embodiment of the present invention, there is provided an ink-jet recording apparatus comprising a first recording unit equipped with a container part which contains an anionic or cationic aqueous ink containing an ultrafinely particulate pigment as a coloring material and an ink-jet head for ejecting the ink, and a second recording unit equipped with a composition container part which contains an aqueous liquid composition containing fine particles dispersed therein and electrically charged at the surface in a polarity opposite to the ink, and an ink-jet head for ejecting the liquid composition.
In a still further embodiment of the present invention, there is provided an ink-jet recording apparatus comprising an ink container part which contains an anionic or cationic aqueous ink containing an ultrafinely particulate pigment as a coloring material, a liquid composition container part which contains an aqueous liquid composition containing fine particles dispersed therein electrically charged at the surface in a polarity opposite to the ink, and ink-jet heads for independently ejecting the ink contained in the ink container part and the liquid composition contained in the liquid composition container part.
In present specification, the term xe2x80x9ca reaction of a coloring material (ultrafinely particulate pigment) with fine particlesxe2x80x9d means ionic bonding, physical/chemical adsorption, absorption, adhesion and any other interaction between both in addition to covalent bonding between both.